The landscape opens into a grey plateau, the self-imposed romance of the day ebbing a touch as we head deeper into Milan’s clogged core. It’s Friday evening, it’s hotter than hell, and as hectoring commuters clamour to inhabit the space we’re currently occupying all effort is invested in not being the first to blink. Directly ahead our genial host, battle-grizzled local Corrado Lopresto, guides his Lancia Florida show queen with gusto, taking a run at what locals call ‘The bridge of broken door mirrors’ without lifting.

Nobody gives an inch so neither do we, trailing in his wake aboard his equally irreplaceable Alfa Romeo Giulietta Spider prototipo and hoping not to fluff a shift on the column change. Our cavalcade is a magnet for the like-minded, or indeed no-minded, the sense of relief on returning the car safely to its lair being of the palpable kind.

Backpedal a few hours and it was a different story. A touch fanciful perhaps, but first sight of this mysterious confection saw us staring in whimpering incomprehension. It does exist! And it’s gorgeous. Memory being an unreliable record where truth is concerned, for decades this car wasn’t even mythical for nobody was even aware of its possible existence. History told us that just one Bertone Giulietta Spider was built, but history was wrong. Unmistakably the work of design colossus Franco Scaglione, and as suggestive of free and easy ’50s glamour as Capri pants and headscarfs, its origins are nonetheless rooted as much in New York as Milano.

Alfa Romeo’s move into the post-war mainstream with the Giulietta depended on so many variables, not least its success Stateside. Which is where Max Hoffman (nee Hoffmann) enters the story. This cultured wheeler-dealer had hitherto held a concession for the marque (among many others) in his native Austria, only to depart for Paris and then New York once the Nazis annexed his homeland. Arriving with greatly reduced means, he nevertheless soon made a bundle selling jewellery made of metal-coated plastic; the enterprising émigré had astutely recognised that women were being employed in factories in huge numbers as part of the war effort and had little to spend their wages on due to shortages. His faux baubles recouped a huge return on his investment.

Emerging from the war considerably better off than when he’d entered it, ‘Maxie’ formed the Hoffman Motor Car Company in 1947. Sited at the crossroads of affluent Park Avenue and 59th Street, his showroom was initially – and predictably - bereft of stock and he took whatever he could get. Yet within three years he had reached agreement with Jaguar to import the XK120 and acknowledged the worth of the VW Beetle after most industry bigwigs had written it off; he briefly held the sole distribution rights for the East Coast. Throw in his role in establishing Porsche in the world’s biggest consumer market, and persuading a sceptical Mercedes-Benz board to produce a road-going version of their gullwing-door Le Mans winner, and it’s clear why he had the ear of most European industry players.

So Alfa Romeo needed Hoffman if it was ever to chase valuable Yankee dollars. Unfortunately, his nose had been put out of joint after an earlier deal to represent the brand Stateside had turned sour before the ink on the concession agreement was dry. A still aggrieved Hoffman was intrigued by talk of the Giulietta but nonetheless rebuffed Alfa’s entreaties. It was only after much wooing that he departed for Italy for a preview of the 750-series Sprint coupé that was due to be launched at the ’54 Turin Salon. He liked what he saw but stipulated that Alfa needed to produce an open-top roadster version. A sceptical management didn’t consider there being much in the way of local demand but, such was Hoffman’s sway in North America, it acquiesced on the proviso that he would act as the marque’s official importer.

Both Pinin Farina and Bertone styling houses were invited to submit proposals. The latter, which only a few years earlier appeared destined for the embalming table, had enjoyed a remarkable reversal of fortune thanks in no small part to backing from American motor mogul Stanley H. ‘Wacky’ Arnolt. That and it landing the gig to style and also build the Giuletta Sprint coupé. Having a genius on the design team – as the design team – didn’t hurt its chances either. Never afraid to buck the herd, Franco Scaglione could think for himself and was arguably the most original stylist of his generation. Resolutely uncompromising about compromising, that same decade would witness his remarkable B.A.T. aerodynamic studies from which some design cues would be transposed intact onto the Spider prototype.

But as we all know by rote, Bertone didn’t land the contract, Pinin Farina’s offering being picked for production by Hoffman on the proviso that it gained wind-up windows. All of which would infer that he disliked the Scaglione car but, for a while at least, it would appear that he entertained the notion of selling both variations on the theme. In fact, the Bertone car only failed because it was deemed too laborious to build. Indeed, company principal Nuccio Bertone admitted many years later that if Scaglione had a failing, it was his inability to think in terms of how his flights of fancy could be replicated. Even so, Hoffman even went as far as to sound out Bertone about the possibility of making the car’s body out of new-fangled wonder material, glassfibre. His response remains unrecorded but somehow you imagine it wasn’t polite.

Bertone’s tender was subsequently forgotten, the firm finding more success with the Sprint Speciale before an argument while at the ’59 Turin Salon prompted Scaglione’s departure. No longer willing to accommodate his artiste’s more capricious tendencies, Nuccio Bertone replaced him with unknown – and unproven – wannabe artist, Giorgetto Giugiaro. The troubled Scaglione consequently became a freelancer, creating such landmark beauties as the Alfa Tipo 33 Stradale while battling an addiction to morphine, a tragic cascade which began with him being invalided during WW2. He would die in obscurity in 1993.

Which was around the time that rumours of this car’s existence began to reach the wider world. The initial prototype had headed Stateside during the ’50s (it now lives in Switzerland), the second example remaining in its homeland. Its early life is sketchy, but it would appear that Pinin Farina received (shortened Guilietta Sprint) chassis one and three, and Bertone numbers two and four. This is chassis four, and it differs significantly from its sibling, most obviously its hind treatment. The rear fins are less pronounced and accommodate the tail light clusters whereby the initial prototype had frenched-in items sited at the edge of the rear deck. ‘Our’ car is believed to have initially lived in Reggio nell’ Amelia and it was only in the early ’80s that stories first began to emerge of its existence by which time it was in a decrepit state. More recently it has benefited from a five-year restoration.

Lopresto, a man whose collecting instincts stretches to 50-plus prototypes and short-run Alfas, Lancias, OSCAs and Isottas, has a near forensic understanding of the Italian motor industry and is a keen advocate of not over-restoring his cars. While the Giulietta wasn’t in great shape when he bought it, he’s since been at pains to retain as much or the original Bertone build as possible. Red as found, the current twin-hues were established on scraping back the blow-over. Inside, the seats have been retrimmed, but the side screens and fabric hood have received nothing more than a good clean. Even the hand-cut (and looks it…) windscreen is original.

And it’s such a captivating shape. Though it doesn’t quite scale the giddy heights of the B.A.T. series, the outline is remarkably free of tinsel for all the showy pretensions. Scaglione’s personal creed of ‘efficiency equals beauty’ is exemplified here, the tapering wing line and vestigial tailfins evoking his earlier Arnolt-Bristol. There’s little to interrupt the flow with even the petrol filler cap being concealed in the boot (unlike on the other car). The bootlid lock, meanwhile, is hidden behind the rear Alfa badge in what would become an Alfa design constant in future decades. It’s truly, really lovely.

Equally so inside, the driver’s seat being comfortable despite little in the way of meaningful butt-shoring. Ahead, standard Giulietta Sprint gauges are housed within a simplistic dash, painted in bronze with a black outline around the binnacle. The Nardi wheel is predictably vast, the overall effect being cool, chic and utterly charming. What’s more, that charm doesn’t evaporate the moment it turns a wheel. All so often concept cars, teasers or whatever you want to call them are built to showcase and forecast ideas.

The actual driving part is secondary, if given any consideration at all. Here there’s none of the expected crashing and banging through the structure. The car’s vintage is obvious but on entertaining back roads it fizzes with raw energy. The 1.3-litre twin-cam ‘four’ revs its little heart out (there’s no red line) and the gear change… Expecting the column shift to be sloppy and slow-witted, it’s nothing of the sort, while the steering is beautifully weighted. Over uneven surfaces there’s the occasional shimmy from out back but otherwise it’s delightful. It’s a Giulietta.

But all too soon it’s back to steeling ourselves for the gauntlet of dread that is Milan in rush hour. Progressing at a rate that would embarrass an asthmatic glacier, there’s plenty of time to ponder if we would be quite so gushing had this fascinating curio actually made production - would familiarity breed, well, over familiarity? Rarity aside, it’s the shape that grabs you. The silhouette was considered daring the better part of 60 years ago and nothing has since dislodged that belief. Scaglione was an original thinker rather than a mere looter of ideas and, while Pinin Farina’s offering was – and remains – achingly pretty, it was rather conservative by comparison. The real shame here is not so much that Bertone’s take wasn’t picked; more that it never got to enchant a wider audience.